An active matrix substrate includes, e.g., thin film transistors (hereinafter also referred to as “TFTs”) as switching elements, one for each pixel, which is the smallest unit of an image.
In order to improve the reliability of an active matrix substrate, TFTs, interconnects, and other components need to be accurately formed on a substrate. For such an active matrix substrate, e.g., patterns of electrodes and interconnects are formed on an insulative substrate to form an uneven surface, and a planarizing film that is an insulating film is formed to cover and planarize the uneven surface. The planarizing film is typically made of, e.g., a spin-on glass (SOG) material, SiO2 in liquid form, or a polymeric film.
Typically, an active matrix substrate includes a gate electrode, a source electrode, and a drain electrode forming portions of a TFT described above, and in order to prevent the electrodes from being excessively etched in an etching step in a manufacturing process, the electrodes are multilayer films each including a plurality of conductive films. For example, a titanium film is formed as a first conductive film that is a lower film of the gate electrode, and a copper film is formed as a second conductive film that is an upper film of the gate electrode. Then, a planarizing film described above is formed on the surface of the gate electrode (see, e.g., PATENT DOCUMENT 1).